In military conflicts there is a constant threat of enemy missles to aircraft. Many of these aircraft are powered by gas turbine engines and some of the missiles seek and home on infrared radiation emitted from exposed hot metal parts and from the hot exhaust plumes of such engines. Particularly when gas turbine engines are utilized in helicopter aircraft it is necessary to provide suppression of infrared radiation under conditions of hover or relatively low flight speed where ram air is not available as a source of cooling air.
Early approaches used to suppress infrared radiation emitted from hot engine parts were directed primarily to the use of sheet metal ducts, or the like, to turn or bend the engine exhaust gas flow path so as to prevent a direct line of sight to the hot engine parts. One design which was employed for this purpose was a simple upturned elbow of circular cross-sectional outline at each position therealong and which served to turn the gas turbine engine exhaust flow upwardly from a ground reference. Although such a simple 90.degree. elbow did serve the purpose of preventing direct viewing of hot metal parts from the ground such an elbow has a serious shortcoming because when utilizing a gas turbine engine to power a helicopter which employs complex flight maneuvers, the hot inside edge of the duct becomes visible for horizontal viewing. Further, the hot exhaust gas plume from a gas turbine which employs such a simple upturned duct or elbow is fully visible.
Other infrared radiation suppressors proposed heretofore have utilized comparatively large center body designs, complex heat transfer panel designs, complicated turning vanes, twisted ducts, or the like. Still others of these previously proposed suppressors utilize air pumps, or the like, to physically pump or otherwise provide cooling air and at a substantial power loss or weight penalty.
Accordingly, the need exists for a simple and economical apparatus for suppressing infrared radiation emitted from hot metal parts from the aft end of a gas turbine engine and from the exhaust gas plume thereof during engine operation.